This invention relates to a bottom block assembly for use in the vertical direct chill (D.C.) casting of metal particularly light metals, such as aluminum.
In the D.C. casting of metals, molten metal is poured into an open-ended tubular mold and begins to solidfy into an ingot. Water is sprayed onto the outside surfaces of the ingot as it emerges from the mold to further cool the ingot and to assist in solidifying the molten metal above the solidified portion of the ingot. At the start of the casting operations, a bottom block or starter block is inserted into the mold bore to seal the discharge end of the tubular mold and to initiate the solidification of the molten metal to form the ingot. Once solidification of the ingot begins, the ingot is urged out of the mold by lowering the bottom block into a pit situated below the casting apparatus. The bottom block may be lowered by hydraulic or other suitable means. In the past, there has been a continual problem with alignment of the bottom block to avoid scuffing, gouging, or other damage to the mold when the bottom block is inserted or withdrawn from the mold.
In a conventional casting station, a plurality of molds (e.g., up to 20 or more) are generally supported on a casting table which can be moved out of position to remove the cast ingots from the pit. A plurality of bottom blocks are rigidly supported on a vertically movable support table. When the support table is raised to insert the bottom blocks into the molds, the operators normally watch for mold movement to determine misalignment of the molds and bottom blocks. Due to the large number of molds at most casting stations, it is impractical for the operators to check each mold to determine if the bottom block is properly aligned. If mold movement is noticed, the raising of the bottom blocks is stopped and the operator, usually by force, repositions the mold. If the mold position cannot be easily adjusted, then the mold would be loosened from the casting table, aligned with the bottom block and refastened to the casting table. In the case of a water-jacketed mold, alignment of the mold and bottom block is more complicated because the coolant and lubricant lines are attached to the mold, and, frequently, these lines would have to be disconnected to position the mold.
Misalignment of the bottom block assembly with respect to the mold can be caused by many various factors. One of the most prevalent is the removal of the ingot from the bottom block assembly after casting. Usually, the bottom block is provided with projections, such as wires, bolt heads and the like, around which metal can solidify so that the bottom block can urge the solidifying ingot out of the mold during the initial period of casting. Shortly after the casting begins, the solidified portion of the ingot is sufficiently heavy to urge the ingot out of the mold and at this point, the bottom block functions to support and control the speed of the ingot withdrawal. When the casting is completed, a lifting device is usually employed to wrench the ingot away from the bottom block. When the ingot is wrenched away from the bottom block, frequently, the bottom would become displaced causing the subsequent misalignment of the bottom block assembly with respect to the mold bore.
In co-pending application Ser. No. 262,509, an improved bottom block design is described and claimed wherein the bottom block is slidably mounted on a support member and is provided with guide members which are adapted to ride guide surfaces positioned below the mold and thereby guide the bottom block into the mold bore. This bottom block assembly was a substantial improvement over conventional bottom block assemblies, but difficulty was experienced in preventing the rotation of the bottom block about the axis of the shaft to which the bottom block support member was affixed. Moreover, when changing over from casting round billets to square or rectangular billets, the mold assembly, bottom block assembly and the guide surfaces had to be changed due to the necessity of the guide surfaces to be uniquely designed for the particular bottom block shape involved.
Against this background, the present invention was developed.